Photosetting resin for making strong, tough resin articles

ABSTRACT

A photosetting resin comprising a liquid monomer composition and a photopolymerization initiator, the monomer composition containing a compound represented by the following formula (1) and a compound represented by the following formula (2) in a weight ratio within the range from 97:3 to 50:50: ##STR1## (wherein R 1  is H or CH 3 , and 0≦m 1  +m 2  ≦4) ##STR2## (wherein R 2  is H or CH 3 , and 5≦n 1  +n 2  ≦12). 
     This photosetting resin can provide a cured resin which is excellent in both strength and toughness.

TECHNICAL FIELD

The present invention relates to a resin which is cured byphotopolymerization. More particularly, the invention pertains to aphotosetting resin which, when used as producing material for resinmolded products, can provide a set or cured material which is excellentin strength as well as in toughness.

BACKGROUND ART

Hitherto, as photosetting resins, there have been used monomercompositions added with a small quantity of a photopolymerizationinitiator, said monomer compositions comprising a polyfunctional monomersuch as 1,6-hexanediol di(meth)acrylate, triethylene glycoldi(meth)acrylate, dicyclopentanyl di(meth)acrylate,tri((meth)acryloxymethyl) isocyanurate, urethane-modifieddi(meth)acrylate, epoxy-modified di(meth)acrylate, trimethylolpropanetri(meth)acrylate and the like, and further, if necessary, with amonofunctional monomer such as methyl (meth)acrylate, ethyl(meth)acrylate, dicyclopentanyl (meth)acrylate, hydroxyethyl(meth)acrylate, N-vinylpyrrolidone and the like.

There are also used colored photosetting resins prepared by adding a dyeor pigment to said photosetting resins and ones added with an organic orinorganic filler to regulate the color tone or mechanical properties ofthe set or cured resins.

These photosetting resins can be set by irradiation of light such asultraviolet light for a short time, from several seconds to severalminutes, to give a desired set or cured resin. Further, most of thesephoto-setting resins are one-pack type and very easy to handle. Theyalso have a characteristic that the thickness where setting takes placeis usually within a range from several μm to several hundred μm, so thatthey find a wide scope of application including, for instance, coatingmaterial, printing ink and adhesive.

Recently, there has been developed a photosetting resin as a materialfor dental use, which can be set with visible light. In the case of thisphotosetting resin for dental use, since visible light is used forsetting the resin, there can be relatively easily obtained a set orcured resin even when the photosetting resin has a large thickness of upto 5-6 mm or is an opaque one mixed with a filler. Accordingly, thistype of photosetting resin is applied advantageously as a filling resinfor cavities or hard resin to be used as resin veneer for cast crown,and for other dental applications.

A need is arising for further expanding the scope of application of thephotosetting resins by making the most of their advantages such asmentioned above. Japanese Patent Application Laying Open (KOKAI)No.58-179212, for instance, discloses a photosetting resin applied as amaterial for producing resin molded products.

However, in application of these conventional photosetting resins toformation of the resin molded products, the obtained molded productswere indeed excellent in surface hardness and other properties such astensile and compressive strength, but generally the molded productswould become hard and fragile so that only a slight flaw to the moldedproduct could result in break thereof.

For instance, in case a photosetting resin having said dicyclopentanyldiacrylate as a monomer component is applied to a hard coating material,there can be obtained a coating film having excellent surface hardness.But in case said photo-setting resin is made into a plate-shaped moldedarticle having a thickness of about 2-3 mm by using a frame, there ismerely obtained a frangible molded article which is easily broken whengiven only a slight deformation.

Such defects of the conventional photosetting resins are due to the verysmall breaking strain of the set or cured resins as noticed in a bendingtest or tensile test of said resins.

Such problem of fragility of the conventional photosetting resins can beovercome by enlarging the breaking strain of the set or cured ones.

But if a monomer having soft properties is simply used as a constituentof a photosetting resin in a bid for attaining said object, although thebreaking strain will be enlarged, there will also arise another problem:sharp reduction of mechanical strength of the set resin, making itimpossible to obtain a molded article having well satisfactorymechanical properties.

Thus, the conventional photosetting resins were frangible and poor intoughness and therefore unsuited for use as a material for formingstrong and tough resin molded articles.

DISCLOSURE OF THE INVENTION

The present inventors have made assiduous studies for solving said priorart problems and, as a result, succeeded in obtaining a toughphotosetting resin by adding a photopolymerization initiator to a liquidmonomer composition comprising, in a ratio by weight of from 97:3 to50:50, a compound represented by the following formula (1) and acompound represented by the following formula (2): ##STR3##

The liquid monomer composition used in the present invention ischaracterized by that, regarding the monomer components constituting thephotosetting resin, bisphenol A di(meth)acrylate having an ethyleneoxide additive molar number of 4 or less is used as the first componentand bisphenol A di(meth)acrylate having an ethylene oxide additive molarnumber in a range from of 5 to 12 is used as the second component.

The present invention will be described in further detail hereinbelow.

Bisphenol A di(meth)acrylate having the ethylene oxide additive molarnumber of 4 or less, which is used as the first component of the monomercomponents constituting the photosetting resin of this invention, is acomponent which serves for affording strength such as tensile andbending strength to the set resin. Bisphenol A di(meth)acrylate havingthe ethylene oxide additive molar number in the range of from 5 to 12,used as the second component of the monomer components, is a componentwhich increases breaking strain of the set resin material.

In the present invention, it is critical that the weight ratio of saidtwo monomer components is within the range from 97:3 to 50:50,preferably from 95:5 to 70:30. If the ratio of the first component ishigher than the above-defined range, although strength of the setmaterial will be high, breaking strain will be lessened to make themolded product frangible. Also, if the ratio of the second componentexceeds the above-defined range, although breaking strain will beincreased, the strength will be excessively lowered and a molded producthaving a desired strength can not be obtained.

Thus, the feature of the present invention resides in that said twomonomer components are used in a weight ratio within the range specifiedin the present invention so as to increase both of strength and breakingstrain.

Therefore, if the ethylene oxide additive molar number of the twomonomer components according to this invention is outside the rangedefined in this invention, the set product of the photosetting resinwill be reduced in strength and/or its breaking strain will be lessened,disadvantageously resulting in unsatisfactory toughness of the setresin.

Regarding the monomer of the first component used in the presentinvention, which is selected from bisphenol A di(meth)acrylates havingthe ethylene oxide additive molar number of 4 or less, it is possible touse in combination, for example, said di(meth)acrylate with said molarnumber of 0 and the one with said molar number of 4. The same is true ofthe second component.

As the photopolymerization initiators usable in the present invention,there can be mentioned ordinary photopolymerization initiators forphotopolymerization by ultraviolet ray such as benzoin ethers,benzophenones, thioxanthones, acetophenones, 1-hydroxycyclohexyl phenylketone and the like. It is also possible to use photopolymerizationinitiators having sensitivity in a visible light region, such as benzyl,camphorquinone, camphorquinone derivatives, thiopyrylium salts and thelike.

It is desirable that the photopolymerization initiator be used usuallyin an amount within a range of from 0.01 to 10% based on the weight ofthe monomer components, but it is especially desirable that said rangeis from 0.05 to 1% in case of producing a molded article having arelatively large thickness.

Further, in the present invention, a tertiary amine or an organicperoxide may be added as reaction assistant, in addition to thephotopolymerization initiator, for the purpose of further enhancing asetting or curing rate. Also, a thermal polymerization inhibitor such ashydroquinone, hydroquinone monometyl ether and the like may be added forthe purpose of improving storage stability of the photosetting resin.

Still further, in the present invention, a monofunctional (meth)acrylatemay be added in a weight ratio within a range of from 90:10 to 40:60,preferably from 80:20 to 60:40 based on the monomer componentsconsisting of said first and second components, for the purpose offurther improving the properties of the photosetting resin.

As examples of said third component, there can be cited methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl(meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl(meth)acrylate, (meth)acrylic acid, hydroxyethyl (meth)acrylate and thelike.

Especially, if methyl methacrylate or ethyl methacrylate is used as thethird component, it will be possible to further enhance toughness of thephotosetting resin of this invention.

In the present invention, an organic or inorganic filler and/or acolorant such as a dye or pigment may be added according to the purposeof use of the product in the same way as used in the conventionalphotosetting resins.

As the inorganic fillers usable in the present invention, there can bementioned silicon dioxide, titanium dioxide, glass powder and the like,which are ordinarily used.

Especially in case the photosetting resin of this invention is appliedas a dental material having a color resembling that of the teeth, it ispreferred to use a filler with a high refractive index such as titaniumdioxide, zirconium dioxide, alumina and the like in a very small amountfor maximizing the toughness characteristic of the resin which is thefeature of the present invention. Use of the filler with a highrefractive index such as mentioned above, even though in a small amount,enables obtainment of an opalescent or translucent resin, namely a resinwith a color closely analogous to that of the teeth. Also, the resin isnot made frangible by use of said filler since the amount of said filleradded is so small that toughness possessed by the photosetting resin ofthis invention is not impaired.

The added amount of the filler with a high refractive index such astitanium dioxide, zirconium dioxide, alumina and the like is preferablydefined to a range of from 0.001 to 1% by weight, more preferably from0.01 to 0.1% by weight.

It is also desirable that an average particle size of said filler with ahigh refractive index is usually in a range of from 0.02 to 1 μm,preferably from 0.05 to 0.5 μm. By defining the average particle size ofthe filler within said range, it will be possible to obtain a resinhaving a desired color tone although the amount of the filler added issmall, and also toughness of the resin won't be impaired.

Thus, by adding the filler with a high refractive index such asmentioned above to the photosetting resin of this invention whileregulating the amount and average particle size of the filler within theabovedefined ranges, it is possible to make a resin having hightoughness, which is the feature of this invention, as well as anaesthetic quality akin to the color tone of the teeth.

A method for setting or curing the photosetting resin of this inventionwill be described below.

For setting or curing the photosetting resin of this invention, therecan be used a commonly-employed type of ultraviolet light source such asa high pressure mercury lamp and ultra-high pressure mercury lamp, butin case of setting a molded product having a large thickness, it isrecommended to prepare a photosetting resin by using aphotopolymerization initiator having sensitivity to visible light and toemploy a light source which generates visible light such as a xenon orhalogen lamp.

Irradiance of the light applied is preferably adjusted to be in a rangeof from 1 to 50 mW/cm², more preferably from 10 to 30 mW/cm².Irradiation time is usually set between one second and about 30 minutes,practically being preferably in a range of from about 30 seconds toabout 20 minutes.

For preparing a resin molded article by using the photosetting resin ofthis invention, a method is employed in which the photosetting resin isfilled in an ordinary molding frame, then light is applied to the resinto cure it. After curing has been completed, the cured product is takenout of the frame.

The frame used here should be the one which allows irradiation withoutthe light being intercepted by the molded product to be cured. Such aframe may be, for instance, the one which is at least partly made ofsuch material as glass, poly-4-methyl-1-pentene, transparentpolypropylene or the like.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described more particularly below withreference to the examples thereof.

EXAMPLES Example 1

66 parts by weight of 2,2'-bis(4-methacryloxyethoxyphenyl)propane and 34parts by weight of 2,2'-bis(4-methacryloxypentaethoxyphenyl)propane wereweighed into a brown glass bottle, followed by addition of 0.5 part byweight of d,l-camphorquinone and 0.75 part by weight of dibenzoylperoxide as a polymerization initiator, and the mixture was stirred wellto give a photosetting resin of this invention.

Then this liquid resin was filled in a polypropylene-made tube, 4.6 mmin inner diameter and 70 mm long, in such a way that no air cells wouldget thereinto, and the packed tube, after sealed, was irradiated withvisible light by using a commercially available visible light irradiator(α-Light mfd. by Morita Tokyo Seisakusho, Ltd.) for 20 minutes to effectpolymerization of the resin.

After completion of irradiation with the visible light, the cured resincomposition was taken out of the tube. The resin thus obtained was hardand transparent.

Both ends of the resulting resin were then cut out to prepare a 40 mmlong rod-like test piece and it was subjected to a three-point bendingtest by using an Instron universal tester. The bending test wasconducted under the following conditions: span length=20 mm, crossheadspeed=0.5 mm/min.

Values for the flexural breaking strain energy per volume werecalculated by dividing the value for the flexural breaking strain energyby the volume of the test piece (π (2.3 mm)² ×20 mm=332 mm³).

The test showed that the resin of the instant example had a bendingstrength of 16.5 kg f/mm² and a flexural breaking strain of 13%, whichindicate excellent strength of the resin. The test also showed aflexural breaking strain energy of 48 kg f·mm, indicating high toughnessof the resin.

The flexural breaking strain energy was determined as an area of thesection where the stress-strain curve obtained in the bending testencompassed the strain axis.

Examples 2, 3 and 4

The photosetting resin samples of this invention were prepared in thesame way as Example 1 by using the monomer compositions indicated by 2,3 and 4 in Table 1, and the prepared photosetting resin samples weresubjected to photopolymerization by visible light irradiation.

The results of the bending test conducted on the resins thus obtainedare also shown in Table 1.

The resulting resins of Examples 2, 3 and 4 all had a high bendingstrength and also showed a large flexural breaking strain energy andexcellent toughness.

Comparative Examples 1 and 2

Homopolymers of 2,2'-bis(4-methacryloxyethoxyphenyl)propane and2,2'-bis(4-methacryloxypentaethoxyphenyl)propane were prepared by thesame operations as in Example 1, and they were subjected to the bendingtest.

The homopolyer of 2,2'-bis(4-methacryloxyethoxyphenyl)propane was highin bending strength but its bending strain was as small as 9%,indicating its hard and frangible characteristic (see R1 in Table 1),while the homopolyer of 2,2'-bis(4-methacryloxypentaethoxyphenyl)propaneshowed a notably large bending strain of 54% but its bending strengthwas as low as 1.9 kg f/mm².

Also, the flexural breaking strain energy of these homopolymers was lessthan half that of the resins obtained in Examples 1-4, indicating poortoughness of said homopolymers.

Comparative Example 3

A resin composition was prepared by following the same procedure asExample 1 while adopting the compositional ratio of the monomers outsidethe range specified in the present invention as shown under R₃ in Table1.

The resin obtained in this example was transparent but rather soft. Thebending test of this resin showed its low bending strength: 13.2 kgf/mm². The flexural breaking strain energy of this resin was also low:36 kg f·mm.

Comparative Example 4

A resin composition was prepared according to the same procedure asExample 1 except for the use of2,2'-bis(4-acryloxydiethoxycyclohexyl)propane as a monomer.

The obtained resin was very soft and showed a large flexural breakingstrain of 17%, which was comparable with those of the resins of Examples2 and 3, but its bending strength was intolerably low: 5.0 kg f/mm².

Also, the flexural breaking strain energy as determined from thestress-strain curve was as low as 18 kg f·mm, indicating poor toughnessof this resin.

Example 5

By the same operations as in Example 1, there was prepared aphotosetting resin of this invention by adding 0.6 part by weight ofd,l-camphorquinone and 0.6 part by weight of N,N-dimethylparatoluidineas a polymerization initiator to a monomer composition consisting of 62parts by weight of 2,2'-bis(4-methacryloxyethoxyphenyl)propane, 18 partsby weight of 2,2'-bis(4-methacryloxypentaethoxyphenyl)propane and 20parts by weight of methyl methacrylate, and the prepared resincomposition was photopolymerized with visible light irradiation in thesame way as in Example 1.

The resin thus obtained was hard and transparent as those of Examples1-4. The bending test of this resin showed that it had a bendingstrength of 19.3 kg f/mm² and a flexural breaking strain of 16%,indicating excellent strength of this resin.

Further, when the flexural breaking strain energy was determined in thesame way as in Example 1, it was as large as 74 kg f·mm, indicatingexcellent toughness of this resin.

Examples 6-10

Base solutions for photosetting resin compositions of this inventionwere prepared with the monomer compositions shown in Table 2 in the sameway as in Example 5, and the prepared base solutions were subjected tophotopolymerization with visible light irradiation in the same way as inExample 5 to obtain the resins.

The results of the bending tests conducted on the thus obtained resinsare also shown in Table 2. Any of these resins showed an excellentbending strength and a proper degree of flexural breaking strain. Theseresins also showed very large flexural breaking strain energy andexcellent toughness.

Comparative Example 5

A base solution for resin composition was prepared in the same way as inExample 5 by adding a polymerization initiator to a monomer compositionconsisting of 80 parts by weight of2,2'-bis(4-methacryloxyethoxyphenyl)propane and 20 parts by weight ofmethyl methacrylate.

This base monomer solution was photopolymerized in the same way as inExample 1 to prepare a resin. The resin was subjected to the bendingtest, which showed a satisfactorily high bending strength of 18.0 kgf/mm², but the flexural breaking strain was as low as 10%, indicatingthe hard and frangible characteristic of this resin. Also, the flexuralbreaking strain energy determined in the same way as described above was40 kg f·mm, which was far smaller than those obtained in Examples 5-10,indicating poor toughness of this resin.

Example 11

In this example is discussed a preparation of a resin for dental use byadding an inorganic filler to a photosetting resin according to thisinvention.

A monomer composition consisting of 55 parts by weight of2,2'-bis(4-methacryloxyethoxyphenyl)propane, 15 parts by weight of2,2'-bis(4-methacryloxypentaethoxyphenyl)propane and 30 parts by weightof methyl methacrylate was mixed with 0.6 part by weight ofd,1-camphorquinone and 0.75 part by weight of dibenzoyl peroxide andthen further added with 0.02 part by weight of titanium dioxide havingan average particle size of 0.26 μm as inorganic filler, and the mixturewas stirred well to prepare a photosetting resin for dental use.

The photosetting resin thus prepared was polymerized by using visiblelight in the same way as in Example 1. The cured resin, beingtranslucent and opalescent, had a close resemblance to tooth enamel andan admirable aesthetic quality.

For the purpose of evaluating aesthetic quality of the cured resin, thephotosetting resin prepared in this Example was filled between twopieces of slide glass, each being made of blue plate glass, with a 0.5mm thick Teflon spacer interposed therebetween, and cured in the sameway as in Example 1. Light transmittance of the cured resin at awavelength of 550 nm was measured by using a spectrophotometer. Theresult showed that the resin of this Example had a light transmittanceof 71%.

The thus obtained resin was also subjected to the bending test ofExample 1, which showed a bending strength of 19.3 kg f/mm², a flexuralbreaking strain of 18% and a flexural breaking strain energy of 92 kgf·mm, which indicated that the resin was excellent in both strength andtoughness.

Example 12

A photosetting resin was prepared by following the same procedure asExample 11 except the amount of the inorganic filler added. Theproperties of the cured resin are shown in Table 3.

The cured resin of this Example was lower in transparency than theproduct of Example 11 and had a color tone resembling that of dentineand an excellent aesthetic quality. Light transmittance of this resindetermined in the same way as in Example 11 was 49%.

The cured resin of this Example also had excellent toughness as notedfrom the results of the bending test shown in Table 3.

Comparative Example 6

In this comparative example is discussed a preparation of a photosettingresin having an aesthetic quality equal to that of the product ofExample 11 by using the conventional techniques.

To a monomer composition consisting of 70 parts by weight of2,2'-(4-methacryloxyethoxyphenyl)propane and 30 parts by weight ofmethyl methacrylate, there was added the same photopolymerizationinitiator as used in Example 11, followed by further addition of 9 partsby weight of silicon dioxide with an average particle size of 0.02 μmwhich is widely used for ordinary dental resins as an inorganic filler,thereby preparing a photosetting resin.

Curing of the photosetting resin thus prepared in the same way as inExample 11 gave a cured resin having an aesthetic quality almost equalto that of the product of Example 11. Light transmittance of this curedresin determined in the same way as in Example 11 was 72%.

However, the bending test of this cured resin showed that although itsbending strength was 18.2 kg f/mm², the flexural breaking strain was assmall as 8% and also the flexural breaking strain energy was as low as19 kg f·mm. Thus, the cured resin of this comparative example was farlower in toughness than the product of Example 11.

Comparative Example 7

For the purpose of preparing a resin having an aesthetic quality equalto that of the product of Example 12, there was prepared a photosettingresin by following the same procedure as Example 12 except for additionof 20 parts by weight of silicon dioxide having an average particle sizeof 0.02 μm used in Comparative Example 6 as an inorganic filler. Theresults are shown in Table 3.

The cured version of the photosetting resin thus prepared had lighttransmittance of 52% and an aesthetic quality equal to that of theproduct of Comparative Example 6.

However, the bending test of the cured resin thus obtained showed thatthe bending strength, flexural breaking strain and flexural breakingstrain energy of this resin were all far less than those of the productof Example 12, and thus said cured resin was weak and frangible.

                  TABLE 1                                                         ______________________________________                                                                             Flexural                                                               Flexural                                                                             breaking                                                               breaking                                                                             strain                                               Bending  Flexural strain energy                                               strength breaking energy per volume                               Composition (kgf/    strain   (kgf ·                                                                      (kgf · mm/                      (wt %)      mm.sup.2)                                                                              (%)      mm)    mm.sup.3)                                ______________________________________                                        1   BPM1/BPM5   16.5     13     48     0.14                                       (66/34)                                                                   2   BPM2/BPM5   18.0     16     60     0.18                                       (80/20)                                                                   3   BPM1/BPM2/  17.0     16     64     0.19                                       BPM3                                                                          (43/42/15)                                                                4   BPM1/BPA6   18.5     14     58     0.17                                       (90/10)                                                                   R1  BPM1 (100)  18.4      9     21     0.06                                   R2  BPM5 (100)  1.9      54     17     0.05                                   R3  BPM1/BPM5   13.2     16     36     0.11                                       (40/60)                                                                   R4  CHM (100)   5.0      17     18     0.05                                   ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                                             Flexural                                                               Flexural                                                                             breaking                                                               breaking                                                                             strain                                               Bending  Flexural strain energy                                               strength breaking energy per volume                               Composition (kgf/    strain   (kgf ·                                                                      (kgf · mm/                      (wt %)      mm.sup.2)                                                                              (%)      mm)    mm.sup.3)                                ______________________________________                                        5   BPM1/BPM5/  19.3     16     74     0.22                                       MMA                                                                           (62/18/20)                                                                6   BPM1/BPM5/  18.8     17     89     0.27                                       MMA                                                                           (47/23/30)                                                                7   BPM1/BPM4/  19.0     14     62     0.19                                       MMA                                                                           (40/15/45)                                                                8   BPM2/BPM5/  18.8     18     84     0.25                                       MMA/EMA                                                                       (54/16/25/5)                                                              9   BPM1/BPA5/  22.3     18     102    0.31                                       MMA/EMA                                                                       (55/12/24/9)                                                              10  BPM1/BPM6/  23.0     17     107    0.32                                       MMA/BMA                                                                       (60/10/24/6)                                                              R5  BPM1/MMA    18.0     10     40     0.12                                       (80/20)                                                                   ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________                                             Flexural                                               Light      Flexural                                                                           Flexural                                                                             breaking                                       Filler  trans-                                                                             Bending                                                                             breaking                                                                           breaking                                                                             strain energy                        Monomer      Amount                                                                             mittance                                                                           strength                                                                            strain                                                                             strain energy                                                                        per volume                           Composition                                                                             Kind                                                                             added                                                                              (%)  (kgf/mm.sup.2)                                                                      (%)  (kgf · mm)                                                                  (kgf · mm/mm.sup.3)         __________________________________________________________________________    11                                                                              BPM1/BPM5/                                                                            TiO.sub.2                                                                        0.02 71   19.3  18   92     0.28                                   MMA                                                                           (55/15/30)                                                                  12                                                                              BPM1/BPM5/                                                                            TiO.sub.2                                                                        0.05 49   19.5  17   90     0.27                                   MMA                                                                           (55/15/30)                                                                  R6                                                                              BPM1/MMA                                                                              SiO.sub.2                                                                        9.0  72   18.2   8   19     0.06                                   (70/30)                                                                     R7                                                                              BPM1/BPM2/                                                                            SiO.sub.2                                                                        20.0 52   11.0   3    7     0.02                                   MMA                                                                           (55/15/30)                                                                  __________________________________________________________________________

Explanation of symbols

BPM1: compound of the formula (1) wherein m₁ and m₂ are 1 and R₁ is CH₃

BPM2: compound of the formula (1) wherein m₁ and m₂ are 2 and R₁ is CH₃

BPM3: compound of the formula (2) wherein n₁ and n₂ are 3 and R₂ is CH₃

BPM4: compound of the formula (2) wherein n₁ and n₂ are 4 and R₂ is CH₃

BPM5: compound of the formula (2) wherein n₁ and n₂ are 5 and R₂ is CH₃

BPM6: compound of the formula (2) wherein n₁ and n₂ are 6 and R₂ is CH₃

BPA5: compound of the formula (2) wherein n₁ and n₂ are 5 and R₂ is H

BPA6: compound of the formula (2) wherein n₁ and n₂ are 6 and R₂ is H

MMA: methyl methacrylate

EMA: ethyl methacrylate

CHM: 2,2'-bis(4-acryloxydiethoxycyclohexyl)propane

BMA: n-butyl methacrylate

As described above, the photosetting resin disclosed in the presentinvention has remarkably improved the defects of the conventionalphotosetting resins which are incapable of maintaining mechanicalstrength unless they are coated thinly on a substrate to form a coatingfilm. The set or cured version of the present photosetting resin hassatisfactorily high toughness by itself. Therefore, the photosettingresin of the present invention can be well applied to the production ofresin molded articles.

Industrial Applicability

The photosetting resin of the present invention fully exhibits itsadvantageous characteristics when it is used for resin molded articleswhich are required to have strength and toughness. More specifically,the photosetting resin of this invention finds its particularly usefulapplication to dental articles such as brackets for orthodontics,denture base, etc., and to precision machine parts such as miniaturegears, pulleys, plastic screws, etc. It can be also used as a moldingmaterial for optical elements such as lens, prisms, etc.

What is claimed is:
 1. A photosetting resin comprising a liquid monomercomposition and a photopolymerization initiator, said resin when curedhaving a minimum value of flexural breaking strain energy per volume ofat least 0.14 kg f mm/mm³, said monomer composition containing acompound represented by the following formula (1) and a compoundrepresented by the following formula (2) in a weight ratio within arange of from 90:10 to 66:34: ##STR4## (wherein R₁ is H or CH₃, and 0≦m₁+m₂ ≦4) ##STR5## (wherein R₂ is H or CH₃, and 5≦n₁ +n₂ ≦12).
 2. Aphotosetting resin according to claim 1 further containing amonofunctional (meth)acrylate in a weight ratio within a range of from90:10 to 40:60 based on the liquid monomer composition.
 3. Aphotosetting resin according to claim 1, containing 0.001 to 1% byweight of a filter selected from titanium dioxide, zirconium dioxide andalumina and having an average particle size of from 0.02 to 1 μm.